| According to the classical crystal growth theory,the supersaturation(a)of the system is the driving force for crystal growth.Different supersaturation dominates the growth of nanomaterials of different topography.In the case of the low supersaturation in the system,crystal growth is driven by screw dislocations.Nanomaterials currently driven by screw dislocations have been widely used in nanoelectronics,nanophotonics,solar energy conversion,and chemical and biological sensing.Our group has used photochemical reduction method to synthesis hierarchical multiple-growth-hillock superstructures of Ag-Ag2O nanoparticles on ZnO.This sample is dominated by the growth mechanism of Burton-Cabrera-Frank(BCF)theory under the induction of screw dislocations.Due to the localized surface plasmon resonance(LSPR)effect of noble metal nanomaterials(especially Ag and Au),it can be widely used in catalysis,surface enhanced Raman spectroscopy(SERS),and biological sensing.Currently,the use of various morphologies of silver nanomaterials as SERS substrates is the research hotspot.In this paper,hierarchical superstructures of Ag-Ag2O-AgO nanoparticles were synthesized by the UV irradiation of silver nitrate solution.The applications of this kind of superstructures as SERS substrates were explored.The main research contents are as follows:(1)Zero-dimensional(OD)hierarchical superstructures of Ag-Ag2O-AgO nanoparticles:OD hierarchical superstructures of Ag-Ag2O-AgO nanoparticles have been synthesized through 254 nm UV-irradiation of the silver nitrate solution.The XRD result indicates that this nanostructure is a mixture of Ag,Ag2O,and AgO.The growth of the superstructures is mainly driven by screw dislocation.We explored the evolution process of the OD superstructures by changing the reaction time.This nanostructure is developed from a cube which each of six faces has spiral dislocation.The screw dislocation grows into multiple layers of hillocks,and then the superstructures grow into a rhombohedral dodecahedron with rough surface.Finally,the surface of the rhombohedral dodecahedron becomes smooth.(2)One-dimensional(1D)hierarchical superstructures of Ag-Ag2O-AgO nanoparticles:We successfully synthesized the 1D hierarchical superstructures of Ag-Ag2O-AgO nanoparticles by changing the concentration of silver nitrate.When the supersaturation is low in the system,1D tube-like nanostructure is driven by axial screw dislocation.As the supersaturation of the system increases,the tube-like nanostructure evolved into rod-like superstructures.In this transformation process,the screw dislocation-driven growth mechanism and the layer-by-layer(LBL)growth mechanism jointly drive the growth of the superstructures where LBL growth mechanism dominates.The limit of detection(LOD)of thiophenol(TP)adsorbed on the surface of the tube-like superstructures is 10-7 mol/L(M).We find that the SERS intensity of TP adsorbed on the surface of aggregated rod-like superstructures is higher than that of islolated rod-like superstructures.(3)Multi-morphological hierarchical superstructures of Ag-Ag2O-AgO nanoparticles:We obtained multi-morphological superstructures of Ag-Ag2O-AgO nanoparticles through 254 nm UV-irradiation of silver nitrate solution containing isopropanol.XRD result shows that the relative content of silver has greatly increased compared with Ag2O and AgO.Using the silver nitrate solution added with isopropanol,we also obtained the OD superstructures.At the same time,linear,flaky,and dendritic superstructures were also obtained.The addition of isopropanol made the supersaturation in the system unstable.We believe that this is mainly due to the volatilization of isopropanol.When the samples are linear,the supersaturation in the system is lower than the first critical supersaturation(?*).The supersaturation required for the sheet-like superstructures is between two critical supersaturations.When the dendritic superstructures is synthesized,the supersaturation in the system is higher than the second critical supersaturation(?**). |
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